Parasites developing in the lymph nodes might alert the body that an invader is present, and activate a protective immune response.

BBC: The malaria parasite is spread by mosquitoes

More broadly, the principle upon which immunisation is based - namely, exposure to a non-harmful version of the naturally occurring infection in order to induce a natural and protective immune response - can be seen to be a far more natural process than the drug- and surgery-based therapies most widely venerated as the main achievements of modern medicine.

BBC: 'The natural benefits of vaccines'

King sometimes still wears a protective vest in response to a fear of reprisal and some genuine threats.

CNN: Rodney King looks back without anger

He has conducted studies on living neurons which suggest that the tau protein is produced in response to oxidative stress, thus lending support to the protective hypothesis.

ECONOMIST: Dementia